Prior art devices of the type having a hydraulic cylinder assembly extending between an axle and a tie rod are well-known in the art. Typical examples are U.S. Pat. No. 2,163,892 and 3,527,316. These patents disclose a double acting hydraulic cylinder assembly having a cylinder secured to the axle and a single piston rod which is secured at one end to the tie rod. As is well-known in the art, this type of cylinder assembly requires a smaller volume of fluid to retract the piston rod one unit of length than to extend the piston rod one unit of length, as the piston rod, which extends only to one side of the piston, occupies part of the internal volume of the cylinder. The prior art, as for example Australian No. 231,417, also recognizes that it is desirable for the cylinder to be secured to the axle for universal movement since the end of the piston rod secured to the tie rod moves in a non-linear path.
Hydrostatic steering units are also well-known in the prior art. One commonly used form of hydrostatic steering unit displaces equal volumes of fluid to the outlet ports when the steering wheel is turned equal amounts to either the right or to the left. Obviously, if the outlet ports of such a commonly used hydrostatic steering unit were interconnected to a conventional cylinder of the type illustrated in the aforementioned patents, the steering response of the vehicle would be uneven. Thus, a turn to the right could be sharper than a turn to the left for corresponding movements of the steering wheel to the right or to the left.
In order to overcome the problems referred to above when utilizing a hydrostatic steering unit with a single rodded steering cylinder, specialized hydrostatic steering units have been proposed, such as that shown in U.S. Pat. No. 3,528,521. Alternatively, special hydraulic circuits may be provided as shown in U.S. Pat. No. 3,497,032.
It has also been recognized that double rodded cylinders may be advantageously used in a power steering system. Various steering configurations have been proposed to utilize the advantages of the double rodded cylinder, and representative examples are shown in U.S. Pat. No. 2,507,106, 2,930,631, 3,480,100, 3,768,585 and 3,782,491. However, applicant is not aware of any prior art which teaches that a double rodded cylinder assembly can be used when the cylinder assembly extends between an axle and a tie rod.